In the use of a numerically controlled (NC) or a computer numerically controlled (ONC) machining center, for example, such as the Model T-30 machining center produced by Cincinnati Milacron, a set of pallets are supported by an indexing table and are selectively moved to a machining station adjacent a vertically and horizontally movable horizontal spindle. A series of machining tool elements are supported by supply magazines and are selectively transferred to the spindle by an automatic tool changer according to a predetermined sequence as determined by the machine or computer program. When such a machining center is used for machining production parts, usually each part is supported by a corresponding specific fixture which is mounted on a pallet at a loading and unloading station.
When it is necessary to machine five or six sides of a part, the part is commonly secured to one fixture plate for machining one to four sides of the part after which the part is removed from the fixture plate and secured in a different orientation to another fixture plate which is mounted on a pallet and then indexed to the machining station. The set up time required for loading and unloading each part onto each fixture plate and for loading and unloading each fixture plate onto the pallet is substantial and significantly increases the total time and cost of machining a part which requires reorientation relative to the spindle to complete all machining operations on the part. Furthermore, each time a part is removed from one fixture plate and mounted on another fixture plate, the part is exposed to the possibility of damaging a machined surface, thus requiring further machining or scrapping of the part.